Devices which use various types of recording disks, such as optical disks, magneto-optical disks, or flexible magnetic-recording disks, are known as disk drive devices. Of these, the hard-disk drive (HDD) has spread widely as a storage device for computers and is becoming an indispensable information-storage device in current computer systems. In addition, HDD applications, such as video recording and playback devices, car navigation systems, or portable telephones, are increasing because of the superior characteristics of HDDs.
A magnetic-recording disk used in an HDD has a plurality of data tracks and a plurality of servo tracks formed in concentric circles on the magnetic-recording disk. A plurality of data sectors containing user data is recorded in each data track. Each servo track contains address information. The servo tracks are constructed from a plurality of servo data regions separated in the circumferential direction; and, one or a plurality of data sectors is recorded between the servo data regions. By accessing the desired data sector in accordance with the address information of the servo data, a magnetic-recording head can write data to a data sector and read data from a data sector.
The magnetic-recording head is formed on a slider; and, the slider is affixed on the suspension of an actuator. The assembly of the actuator and the head-slider is referred to as a head-stack assembly (HSA). In addition, the assembly of the suspension and the head-slider is referred to as a head-gimbal assembly (HGA). By balancing the pressure due to the viscosity of the air between the air bearing surface of the slider disposed in proximity to the recording surface of the a rotating magnetic-recording disk with a load applied in the direction of the magnetic-recording disk by the suspension, the head-slider can fly above the magnetic-recording disk. By swinging the actuator about the pivot shaft, the head-slider moves to the target track and is positioned above that track.
With the advance of HDD technology, accompanying an increase in the tracks per inch (TPI) of the magnetic-recording disk, the positioning precision of the head-slider is also increased. However, the actuator driven by a voice coil motor (VCM) has limited positioning precision. Therefore, technology for a dual-stage actuator that is equipped with a compact actuator, known by the term of art “microdrive actuator,” has been incorporated in the rotary actuator and provides for finer positioning of the magnetic-recording head. Therefore, engineers and scientists engaged in HDD manufacturing and development are interested in finding ways to more accurately control the positioning of the dual-stage actuator.